Add test for small surface instability condition with no EL.
Add test for small surface instability condition with no EL.

ahaberlie/MetPy,dopplershift/MetPy,jrleeman/MetPy,ShawnMurd/MetPy,jrleeman/MetPy,ahaberlie/MetPy,Unidata/MetPy,dopplershift/MetPy,Unidata/MetPy